In April, Williams was arrested on felony charges of burglary with assault or battery and aggravated assault with a deadly weapon without intent to kill, stemming from the December incident.
Police records show she struck ex-girlfriend Alkeria Davis in the head and pulled her hair after Davis opened the front door of her house on Dec. 6. After a man at the home broke up the altercation, Williams reportedly went to her car and pulled out a gun, pointed it in the man's direction and said "You'll get all 18" before leaving the scene.
The criminal case is ongoing.
In announcing the suspension, the WNBA said it conducted its own investigation and consulted with domestic violence experts before deciding on the 10-game ban.
"Based on the investigation, consultation, and a careful weighing of all the facts and circumstances, the WNBA determined that a ten-game suspension was appropriate," the league said. "Among other factors, the WNBA took into account the nature and seriousness of the conduct at issue, including the involvement of a firearm."
Williams also must participate in counseling, per the league.
"As an organization, we abhor violence of any kind and specifically take domestic violence allegations very seriously," the Sparks said in a statement. "We will provide whatever resources we are allowed to help Riquna learn and grow from this unfortunate situation."
The union said it would file a grievance on Williams' behalf.
"We are disappointed with the league's actions. There is an ongoing criminal proceeding and in fairness to the player, the league could have and should have awaited its completion before taking any action,'' said Terri Jackson, executive director of the union.
"Riquna has not had a fair opportunity to fully defend herself. We are immediately filing a grievance and will seek the arbitrator's review.''
The suspension surpassed the seven games given to Brittney Griner and Glory Johnson in 2015 for their domestic violence arrests. It's not the longest suspension in league history, however: The WNBA dismissed Rhonda Mapp, who also played for Los Angeles, in 2003 for violating its drug policy. Mapp never returned after being suspended by the league for two years.
Williams is in her seventh WNBA season. The Sparks re-signed her in May despite the charges. In 15 games, she is averaging 11.5 points this season.
Her suspension will begin Thursday when the Sparks play the Dallas Wings.
The WNBA also is investigating Seattle Storm forward Natasha Howard after her wife made domestic abuse allegations on social media on Saturday.
The Associated Press contributed to this report.
Winters-Scott pleased with WNBA suspending Williams 10 games
NBC Sports Washington basketball analyst Christy Winters-Scott joins OTL to share her reaction to Riquna Williams' 10-game suspension for a domestic violence incident.